1. Field of the Invention
Embodiments of the present invention relate to methods of operating and calibrating acoustic sand detectors, and a method of determining the life expectancy of a flowline. Embodiments of the present invention are particularly suitable for implementation with production flowlines of hydrocarbon wells, for example subsea hydrocarbon production wells.
2. Description of the Prior Art
Production fluid from fluid extraction wells, for example underwater hydrocarbon extraction wells, typically have solid particles such as sand entrained within it. The impact of these particles on the walls of production fluid flowlines, which carry the fluid to the surface, is known to erode the walls. If this erosion is unchecked, the flowline may fail, and leak production fluid to the surrounding region.
The level of erosion will be dependent on various factors, with the most important being the quantity of sand entrained within the fluid. It is therefore desirable to be able to monitor the level of sand within the fluid, to estimate the erosion of the flowline.
To this end, acoustic sand detectors have been commonly used to detect sand, by listening to the impact of the particles on the pipe wall. However, the output of such detectors does not give a clear indication of the levels of sand within the flow, since not all the sand will create a detectable impact in the vicinity of the detector. It is therefore desirable to provide effective calibration of these detectors. However, proper calibration by the manufacturers is difficult due to a number of factors, for example: different types of sand, e.g. with differing grain sizes or density; different environments, e.g. pipe differences leading to differing levels of acoustic signal damping, or internal fluid differences, or background noise; and imprecise knowledge of the exact location where sand hits the wall, e.g. due to flow properties and sand type.
In addition, the above variables may not only be hard to predict, but may also change substantially over the life of a production field, making the measurement from the detectors even more inaccurate.
It is an aim of the embodiments of the present invention to overcome these problems. This aim is achieved by improving the operation and calibration of acoustic sand detectors using local flow characteristics.